25,162 research outputs found
Analytical and finite-element study of optimal strain distribution in various beam shapes for energy harvesting applications
Due to the increasing demand for harvesting energy from environmental vibration, for use in self-powered electronic applications, cantilever-based vibration energy harvesting has attracted great interest from various parties and become one of the most common approaches to convert redundant mechanical energy into electrical energy. As the output voltage produces from a piezoelectric material depends greatly on the geometric shape and the size of the beam, there is a need to model and compare the performance of cantilever beams of differing geometries. This paper presents the study of strain distribution in various shapes of cantilever beams, including a convex and concave edge profile elliptical beams that have been overseen in most of the prior literature. Both analytical and finite element models are derived and the resultant strain distributions in the beam are computed based on MATLAB solver and ANSYS finite element analysis tools. An optimum geometry for a vibration-based energy harvester system is verified. Lastly, experimental results comparing the power density for a triangular and rectangular piezoelectric beams are also presented to validate the finding of the study and the claim as suggested in the literature is verified
Spinless Topological Insulators without Time-Reversal Symmetry
We explore the 32 crystallographic point groups and identify topological
phases of matter with robust surface modes. For n =3,4 and 6 of the C_{nv}
groups, we find the first-known 3D topological insulators without spin-orbit
coupling, and with surface modes that are protected only by point groups, i.e.,
not needing time-reversal symmetry. To describe these C_{nv} systems, we
introduce the notions of (a) a halved mirror chirality: an integer invariant
which characterizes half-mirror-planes in the 3D Brillouin zone, and (b) a bent
Chern number: the traditional TKNN invariant generalized to bent 2D manifolds.
We find that a Weyl semimetallic phase intermediates two gapped phases with
distinct halved chiralities
Parafermionic phases with symmetry-breaking and topological order
Parafermions are the simplest generalizations of Majorana fermions that
realize topological order. We propose a less restrictive notion of topological
order in 1D open chains, which generalizes the seminal work by Fendley [J.
Stat. Mech., P11020 (2012)]. The first essential property is that the
groundstates are mutually indistinguishable by local, symmetric probes, and the
second is a generalized notion of zero edge modes which cyclically permute the
groundstates. These two properties are shown to be topologically robust, and
applicable to a wider family of topologically-ordered Hamiltonians than has
been previously considered. An an application of these edge modes, we formulate
a new notion of twisted boundary conditions on a closed chain, which guarantees
that the closed-chain groundstate is topological, i.e., it originates from the
topological manifold of degenerate states on the open chain. Finally, we
generalize these ideas to describe symmetry-breaking phases with a
parafermionic order parameter. These exotic phases are condensates of
parafermion multiplets, which generalizes Cooper pairing in superconductors.
The stability of these condensates are investigated on both open and closed
chains.Comment: 27 pages, 9 figure
Do criminal sanctions deter insider trading?
Many developed markets have taken what appears to be a tough stance on illegal insider trading through the use of criminal sanctions. Although criminal sanctions represent a much greater penalty than civil sanctions, the higher burden of proof required makes their enforceability weaker. This trade-off between severity and enforceability makes the impact of criminal sanctions ambiguous. In this paper, we empirically examine this issue by studying the deterrence of insider trading following the introduction of criminal sanctions in a developed market. Significant changes in sanction regimes are rare, especially when criminal sanctions are introduced without other changes. In February 2008, New Zealand introduced criminal sanctions for insider trading. This change of law offers a unique setting in which to examine the deterrence effect of criminalization. Using measures for the cost of trading, degree of information asymmetry, and probability of informed trading, we find that the enactment of this law led to a worsening in these measures. These findings suggest that the weaker enforceability of criminalization outweighs the associated increased severity of the penalties
Exons, introns and DNA thermodynamics
The genes of eukaryotes are characterized by protein coding fragments, the
exons, interrupted by introns, i.e. stretches of DNA which do not carry any
useful information for the protein synthesis. We have analyzed the melting
behavior of randomly selected human cDNA sequences obtained from the genomic
DNA by removing all introns. A clear correspondence is observed between exons
and melting domains. This finding may provide new insights in the physical
mechanisms underlying the evolution of genes.Comment: 4 pages, 8 figures - Final version as published. See also Phys. Rev.
Focus 15, story 1
Measurement techniques for cryogenic Ka-band microstrip antennas
The measurement of cryogenic antennas poses unique logistical problems since the antenna under test must be embedded in a cooling chamber. A method of measuring the performance of cryogenic microstrip antennas using a closed cycle gas cooled refrigerator in a far field range is described. Antenna patterns showing the performance of gold and superconducting Ka-band microstrip antennas at various temperatures are presented
Staying true with the help of others: doxastic self-control through interpersonal commitment
I explore the possibility and rationality of interpersonal mechanisms of doxastic self-control, that is, ways in which individuals can make use of other people in order to get themselves to stick to their beliefs. I look, in particular, at two ways in which people can make interpersonal epistemic commitments, and thereby willingly undertake accountability to others, in order to get themselves to maintain their beliefs in the face of anticipated “epistemic temptations”. The first way is through the avowal of belief, and the second is through the establishment of collective belief. I argue that both of these forms of interpersonal epistemic commitment can function as effective tools for doxastic self-control, and, moreover, that the control they facilitate should not be dismissed as irrational from an epistemic perspective
Stimulated Raman adiabatic passage analogs in classical physics
Stimulated Raman adiabatic passage (STIRAP) is a well established technique
for producing coherent population transfer in a three-state quantum system. We
here exploit the resemblance between the Schrodinger equation for such a
quantum system and the Newton equation of motion for a classical system
undergoing torque to discuss several classical analogs of STIRAP, notably the
motion of a moving charged particle subject to the Lorentz force of a
quasistatic magnetic field, the orientation of a magnetic moment in a slowly
varying magnetic field, the Coriolis effect and the inertial frame dragging
effect. Like STIRAP, those phenomena occur for counterintuitively ordered field
pulses and are robustly insensitive to small changes in the interaction
properties
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